1. Field of Invention
The present invention relates generally to the electrochemical plating of articles and more particularly to means for testing the efficacy of such plating.
2. Description of the Prior Art
The automotive industry makes widespread use of decorative chromium plated parts on exterior surfaces. It is common industry practice to plate such parts in multiple layers employing duplex nickel and chromium to protect the base material of the part from corrosion while presenting an attractive appearance.
The prevention of premature failure of the protective plating layers to perform this function is a matter of extensive, expensive, and continuous effort in the industry. To this end certain criteria have been developed for evaluating the long term corrosion resistance of duplex nickel and chromium plated parts. Among these are adequate nickel thickness, appropriate ratio of semibright to bright nickel thickness, and satisfactory electrochemical potential difference and polarity between the semibright and bright nickel layers.
Suitable means to measure the total thickness of the combined nickel layers such as by deplating (coulometric stripping) is well known and widely used in the industry. The necessity for determination of the individual nickel layer thicknesses and thickness ratio, however, while well known, involves the use of microscopic techniques which are both tedious and time consuming. Use of such techniques is therefore rather expensive and consequently use in the prior art has been severely limited. Even more laborious and difficult to determine is interlayer electrochemical potential difference and polarity, which consequently has meant that such determinations have practically never been made. This nondetermination of a relevant criterion has often resulted in misdiagnosis of the failure mechanism of a prematurely corroded part.